1. Field of the Invention
This invention relates to downhole well tools and, in particular, to a survey apparatus adopted to ascertain the angular orientation of a drilling tool with respect to a predetermined datum.
2. Description of the Prior Art
In directional drilling work it is often desirable to ascertain the direction in which a deflectable drilling element is oriented with respect to a predetermined datum. It is only by ascertaining this orientation that drilling operators on the surface can accurately determine if the directional drilling procedure is being effectuated in accordance with a predetermined drilling plan. To this end there is usually provided in a predetermined axial alignment with the deflectable drilling element a key member projecting radially inwardly into the interior of the drill string of which the deflectable drilling element is the lowermost constituent element.
To periodically ascertain the orientation of the deflectable drilling element it is necessary to lower into the interior of the drill string a suitable bottom hole directional survey apparatus. The survey apparatus generally includes a survey instrument of a standard type, typically comprising a magnetic compass, a transparent glass ring having a plurality of concentric circles scribed thereon, as well as a radially extending reference indicator line, a camera and a light source. The lowermost constituent element of the survey apparatus is usually a mule shoe element. The reference line within the instrument is angularly aligned with an axially extending slot provided in the mule shoe element.
Since the reference line in the survey instrument is angularly aligned with the slot in the mule shoe, when the survey apparatus is lowered or pumped down into the interior of the drill string, engagement of the key with the slot in the mule shoe guarantees axial alignment between the reference indicator line in the instrument, the slot in the mule shoe, the key engaged therewith, and the deflectable drilling element having the key. In this manner, an accurate indication of the magnitude of the deviation (if any) between a predetermined angular datum and the actual orientation of the deflectable drilling element may be obtained.
It is, therefore, of utmost importance that prior to the lowering or pumping down of the survey apparatus accurate axial alignment be established between the slot in the mule shoe and the reference line scribed within the instrument. Prior art, such as U.S. Pat. No. 3,052,309 (Eastman), provides for the orientation and alignment of the reference line in the instrument with the slot in the mule shoe by the utilization of liquid leveling clamps. Further, the last-mentioned Eastman patent describes means for adjustably orienting the mule shoe with the reference line to permit any predetermined number of axially elongated, non-magnetic, spacer elements to be threaded into the bottom hole survey apparatus between the instrument and the mule shoe. This adjustable arrangement includes a lock nut disposed upon an orienting lug to permit threaded adjustment of the angular orientation of the lug with respect to the survey apparatus. The lug exhibits a predetermined shape adapted to be received in a keyway provided in the lower end of the instrument. It is appreciated that by the provision of such an adjustable locking arrangement using an orienting lug assembly in cooperation with a threaded locking nut the reference line in the instrument may be aligned axially and angularly with the slot in the mule shoe, even if a variable number of non-magnetic spacer elements are interposed therebetween. However, it is also appreciated that it is necessary to disassemble the survey apparatus to gain access to the adjustment arrangement each time it is decided to shorten or elongate the apparatus by the addition or removal of spacers. Of course, the spacers are required to define a non-magnetic portion of the survey apparatus sufficient to permit the magnetic compass disposed within the instrument to function reliably.
U.S. Pat. No. 2,956,781 (Eastman) defines a prior art deflecting tool, the orientation of which a survey apparatus is utilized to ascertain. U.S. Pat. No. 2,819,039 (Lindsay) and U.S. Pat. No. 2,819,040 (James) further illustrate deflecting tools known in prior art. U.S. Pat. No. 3,122,213 (Hawk) discloses an apparatus for orienting a tool in a well bore.
U.S. Pat. No. 2,088,539 (Stokenbury) relates to a method and apparatus for orienting a deflecting tool within a well bore by the utilization of axially spaced peep sights. U.S. Pat. No. 2,207,505 (Bremner) and U.S. Pat. No. 2,246,417 (Smith) relate to drill pipe orienting tools. Bremner generally discloses the utilization of scribe lines on adjacent tool elements such that threaded engagement therebetween disposes the scribe lines in next-axial alignment to insure the proper axial relationship between the next-adjacent elements. It is noted that the apparatus shown in Bremner is unable to be utilized if the scribed elements are axially spaced, as by a plurality of spacers, one from the other. Smith discloses a threadedly adjustable orienting tool whereby axial alignment between members may be adjusted by threaded rotation of one member with respect to another. Although Smith provides as an advantage the adjustability of the members by an externally accessible threaded engagement therebetween, no locking arrangement other than the frictional fit of engaged threads is disclosed, taught or suggested.
U.S. Pat. No. 1,815,319 (McCoy) relates to a method for diverting a well drilling tool. U.S. Pat. No. 2,318,590 (Boynton) discloses threaded lock arrangement utilizing a plurality of circumferentially disposed splines. Other patents relating to the orientation of a bore hole device include U.S. Pat. No. 3,718,194 (Hering), U.S. Pat. No. 3,175,608 (Wilson, relating to directional tubing perforation), U.S. Pat. No. 3,363,703 (Shewmake, relating to a coring tool), U.S. Pat. No. 3,450,216 (Hugel, relating to a core orienting apparatus) and U.S. Pat. No. 2,207,507 (Douglas, relating to a telltale). Other patents relating generally to the orientation of a bore hole include U.S. Pat. Nos. 3,633,280 and 3,711,118 (both to Lichte). U.S. Pat. Nos. 3,215,204 (Sims) and 3,339,636 (Frisby) both relate to a whipstock. U.S. Pat. Nos. 3,068,946 and 3,156,310 (both to Frisby) relates to knuckle joints.
It would be advantageous to provide a survey apparatus whereby alignment between a reference indicator line disposed within the survey instrument may be aligned with an axially extending slot provided in a mule shoe element in an expeditious and accurate manner after the assembly and connection of the survey tool is completed. It would be of further advantage to be able to provide such alignment without the necessity of disassembling the apparatus to gain access to a locking arrangement which utilizes a lug receivable within a keyway in the instrument itself. Furthermore, it would be advantageous to provide an externally accessible adjusting arrangement to facilitate the alignment of a reference line and a slot in the mule shoe whenever spacers are added or withdrawn from the survey apparatus. It would be also advantageous to utilize visual means, such as sights or the like, the expeditiously orient the members in order to insure alignment between the reference line in the instrument and the slot in the mule shoe.
It would also be of advantage to provide a bottom hole survey apparatus having a torque transmitting sub therein utilizing a predetermined plurality of axially spaced sets of splines, each set containing a predetermined number of splines with corresponding splines in each set being angularly offset such that any predetermined one of the sets of splines may be selectively engaged with an array of grooves disposed on the interior of a member so that the reference line may be oriented with the slot in the mule shoe within a predetermined tolerance and yet be securely affixed in a torque-transmitting relationship.